This invention relates to a method of and a system for delivering water-based explosives, especially into blastholes.
The most widely used mass method for underground blasthole charging is by the pneumatic loading of ANFO (ammonium nitrate fuel oil). ANFO is a solid particulate explosive and is favoured for comparative cost, ease of use and the simple equipment required to load it into blast holes.
There are however several disadvantages to the use of ANFO. It is not water-resistant and cannot be applied effectively in wet mines. It is easily spilled and pneumatic loading or charging may result in a high percentage of blowouts affecting the quality of wastewater. Blowout dust is also a respiratory and skin irritant. Furthermore, being a straight mixture of ammonium nitrate and a fuel oil there is not much flexibility in the formulation, and blast manipulation to achieve the desired results is limited to mining practice, for example changing the burden and spacing of the pattern of boreholes.
Water-based explosives such as water-in-oil emulsion and so-called watergel explosives are two common underground mining explosive types which are used as alternatives to ANFO. These products have the advantage of being water-resistant. They can also be formulated with a wide range of available energy per unit volume, which is an important property of explosives. They are generally used in underground mining in cartridged form. The process of charging and consolidating explosive cartridges into a borehole is labour intensive, and it has been known to cause serious accidents if not done with sufficient care. Various methods and apparatus are in use for the direct charging of these explosive types from a mass container into blast holes. A disadvantage of current methods of direct charging of these explosive types is that detonative continuity is provided by the explosive from the blast hole to the mass container. Accordingly most of these methods employ the feed of non-explosive components from the mass container to a point near charging where the non-explosive components are mixed with a sensitiser to become explosive in the borehole. The most common approach with emulsion explosives is the admixture of a gassing component into the delivery hose near to the point of charging. The gassing component undergoes a chemical gassing reaction with the emulsion, thereby sensitising it to a detonative level.
Detonative continuity from the blast hole to the holding or mass container is interrupted by virtue of the insensitivity of the hose content between the mass container and the admixture of the gassing component. Disadvantages of this process include the fact that the integrity and quality of the explosive in the blasthole depends on the effectiveness of mixing the sensitiser with the non-explosive mixture. Mixing devices in these systems have the added disadvantage of increasing pump delivery pressures. Pumping pressures can be reduced by the use of water to form an annulus in the delivery hose, which acts as a lubricant, but only provided the annulus is maintained.
It is accordingly an object of the present invention to provide an alternative method of delivering fluid explosives and to provide a system for performing this method.
According to the present invention there is provided a method of delivering a water-based explosive comprising:
feeding a water-based explosive and a fluid non-explosive carrier into a tubular delivery member in order that the water-based explosive defines a plurality of bodies separated from each other by the carrier; and
feeding the bodies of water-based explosive separated by the carrier through the tubular delivery member to a point of delivery.
Preferably the water-based explosive and carrier is fed into the delivery member in order that the water-based explosive defines a plurality of bodies separated from each other by the carrier to ensure that detonative continuity is not present in the delivery member.
Since the water-based explosive is delivered as a plurality of bodies separated by the non-explosive carrier it is easy to arrange, by simply varying the relative quantities of explosive and carrier, that detonative continuity is interrupted in at least one position between the point of delivery and point at which the water-based explosive is fed into the delivery member. This can be effected by having a higher feed rate of carrier fluid than a water-based explosive.
The water-based explosive and carrier may be fed into the delivery member to form a number of columns of water-based explosive, interrupted and separated by the carrier. Preferably the carrier also forms an annulus in the tubular delivery member through which the columns of water-based explosive pass in order to provide lubricity between the explosive and the wall of the tubular delivery member. Alternatively the water-based explosive and carrier may be fed into the delivery member to form a plurality of smaller bodies. This is especially the case where the carrier fluid comprises a gas.
The water-based explosive and carrier may be fed into the delivery member by means of an enveloper comprising a hollow body with an inlet for the carrier, an inlet for the explosive, and a joint outlet for the carrier and explosive; the arrangement being such that the carrier in use breaks up the explosive into bodies separated by the carrier which leave the enveloper through the outlet. Alternatively the water-based explosive and/or carrier may be fed in alternating fashion into the delivery member. This may be achieved by interrupting the feed of the water-based explosive and/or carrier into the delivery member in an alternating fashion. Preferably the feed of both the water-based explosive and carrier is interrupted and preferably the feed is interrupted in a synchronised alternating sequence resulting in alternate delivery of explosive and carrier into the delivery member. The interruption may be effected by a suitable valve arrangement.
The water-based explosive may comprise an emulsion explosive or an emulsion explosive containing other ingredients such as ammonium nitrate and/or aluminium. Alternatively it may comprise a watergel explosive. In all cases the water-based explosive may be chemically altered, for example by cross-linking, in such a way that it sets into a semi-rigid body after it is ejected from the tubular delivery member.
The water-based explosive may be viscous, even highly viscous and the viscosity of the water-based explosive may fall in the range from 40 000 cps to 700 000 cps preferably from 250 000 to 500 000 cps.
The water-based explosive may be sensitised for direct use in blastholes in which it is intended to be used. Although aforementioned is a preferred embodiment, additional sensitiser may be added prior to delivery of the water-based explosive.
The water-based explosive may be sensitive to initiation by booster or priming charge, but may also be sensitive to initiation by standard commercial detonators.
The carrier fluid may comprise a liquid and preferably it comprises water. In such cases the water-based explosive comprises a water resistant explosive. The carrier liquid may also be suitable to lubricate the passage of the water-based explosive through the delivery member. Water as carrier liquid serves as such a lubricant.
Alternatively the carrier fluid may comprise a gas and preferably the gas includes a lubricating agent for lubricating the passage of the water-based explosive through the delivery member. The lubricating agent may comprise water. In one preferred embodiment of the invention the carrier gas may comprise water-wet air.
1.2:1.
The water-based explosive and carrier in gaseous form may be fed into the delivery member at a carrier to explosive ratio from 2000:1 to 60000:1, preferably from 4500:1 to 18000:1 (volume basis) with the gas carrier volume being expressed (volume basis) with the gas carrier volume being expressed at standard temperature and pressure.
The water-based explosive may be fed under a pressure from 10 kPa to 600 kPa. preferably from 20 kPa to 400 kPa. And most preferably about 50 kPa to 240 kPa.
The carrier may be fed under pressure from 20 kPa to 650 kPa, preferably from 50 kPa to 400 kPa and most preferably about 100 kPa to 250 kPa.
In one embodiment of the invention the carrier may be fed into the delivery member in a manner to break up a column of the water-based explosive into discontinuous subsections. Preferably the subsections have diameters which are slightly smaller than the internal diameter of the tubular delivery member.
The tubular delivery member may comprise a pipe, including a hose.
The water-based explosive may be delivered into a blasthole, including a blasthole with a diameter of smaller than 100 mm. The water-based explosive is preferably sensitised for direct use in such blastholes, without the need to add additional sensitiser prior to delivery into such blastholes.
According to another aspect of the present invention there is provided a system for delivering a water-based explosive comprising:
feed means for feeding a water-based explosive;
feed means for feeding a fluid non-explosive carrier; and
a mixing arrangement for mixing and providing the water-based explosive and carrier in a tubular delivery member in order that the water-based explosive defines a plurality of bodies separated from each other by the carrier.
The feed means for feeding the water-based explosive may comprise any suitable feed means, such as a pressurised vessel with an outlet through which the explosive may be fed, or a pump arrangement.
The feed means for feeding the carrier may comprise a source of fluid under pressure being fed through suitable conduits.
The mixing arrangement may comprise means for bringing together the fed explosive and carrier under conditions allowing a plurality of bodies of the water-based explosive to form. The conditions may be provided by regulating aspects such as feed ratio and pressures under which the water-based explosive and carrier are fed.